SURF151 Element Description

SURF151 may be used for various load and surface effect applications. It may be overlaid onto a face of any 2-D thermal solid element (except axisymmetric harmonic elements PLANE75 and PLANE78). The element is applicable to 2-D thermal analyses. Various loads and surface effects may exist simultaneously. See SURF151 in the Mechanical APDL Theory Reference for more details about this element.

Figure 151.1:  SURF151 Geometry

SURF151 Input Data

The geometry, node locations, and the coordinate system for this element are shown in Figure 151.1: SURF151 Geometry. The element is defined by two to five node points and by the material properties. The nodes for this element must share the nodes of the underlying solid element. An extra node (away from the base element) may be used for convection or radiation effects. Two extra nodes (away from the base element) may be used to more accurately capture convection effects.

The mass, volume, and heat generation calculations use the in-plane element thicknesses at nodes I and J (real constants TKI and TKJ, respectively). Thickness TKI defaults to 0.0, and thickness TKJ defaults to TKI. If KEYOPT(3) = 3, the out-of-plane thickness is input as the real constant TKPS (defaults to 1.0). The mass calculation uses the density (material property DENS).

See Nodal Loading for a description of element loads. Convections or heat fluxes may be input as surface loads on the element.

The convection surface conductivity matrix calculation uses the film coefficient (input on the SFE command with KVAL = 0 and CONV as the label). If the extra node option is used, its temperature becomes the bulk temperature. If the extra node is not used, the CONV value input with KVAL = 2 becomes the bulk temperature. The convection surface heat flow vector calculation uses the bulk temperature. On a given face, either a heat flux or a convection may be specified, but not both simultaneously.

For the extra node option (KEYOPT(5) = 1), film effectiveness and free stream temperatures may also be input for convection surface loads (input on the SFE command with the CONV label and KVAL = 3 and 4, respectively). If film effectiveness is input, bulk temperature is ignored.

Setting KEYOPT(7) = 1 multiplies the evaluated film coefficient by the empirical term ITS-TBIⁿ, where TS is the element surface temperature, TB is the fluid bulk temperature, and n is an empirical coefficient (real constant ENN).

Convections and heat fluxes are multiplied by an area to obtain the heat flows. KEYOPT(12) determines whether the current area or the original area is selected for the calculation.

If KEYOPT(5) = 1 and flow information is available from FLUID116 with KEYOPT(2) = 1, the bulk temperature may be adjusted to the adiabatic wall temperature using KEYOPT(6) = 1, real constants OMEG (rotational speed) and NRF (recovery factor), and the logic described in the Mechanical APDL Theory Reference. For this adjustment, the global Y Cartesian coordinate axis is used as the axis of rotation (KEYOPT(3) = 1). When using the OMEG real constant, you can specify either numerical values or table inputs. If specifying table inputs, enclose the table name in % signs (for example, %tabname%). Rotational speed (OMEG) can vary with time and location. Use the *DIM command to dimension the table and identify the variables. For more information and examples on using table inputs, see Array Parameters of the ANSYS Parametric Design Language Guide, Applying Loads Using TABLE Type Array Parameters in the Basic Analysis Guide and Doing a Thermal Analysis Using Tabular Boundary Conditions in the Thermal Analysis Guide, as well as the description of *DIM in the Command Reference.

A film coefficient specified by the SFE command may be modified by activating the user subroutine USERCV with the USRCAL command. USERCV may be used to modify the film coefficient of a surface element with or without an extra node. It may be used if the film coefficient is a function of temperature and/or location.

If the surface element has an extra node (KEYOPT(5) = 1), the bulk temperature and/or the film coefficient may be redefined in a general way by user programmable routine USRSURF116. USRSURF116 may be used if the bulk temperature and/or the film coefficient is a function of fluid properties, velocity and/or wall temperature. If a bulk temperature is determined by USRSURF116, it overrides any value specified by SFE or according to KEYOPT(6). Also, if a film coefficient is determined by USRSURF116, it overrides any values specified by SFE or USRCAL, USERCV. USRSURF116 calculation are activated by modifying the USRSURF116 subroutine and creating a customized version of ANSYS; there will be no change in functionality without modifying USRSURF116. For more information, see User-Programmable Features (UPFs) in the Mechanical APDL Advanced Analysis Guide.

Heat generation rates are input on a per unit volume basis and may be input as an element body load at the nodes, using the BFE command. Element body loads are not applied to other elements connected at the same nodes. The node I heat generation HG(I) defaults to zero. The node J heat generation defaults to HG(I). The heat generation load vector calculation uses the heat generation rate values.

As an alternative to using the BFE command, you can specify heat generation rates directly at the nodes using the BF command. For more information on body loads, see Body Loads in the Basic Analysis Guide.

SURF151 allows for radiation between the surface and the extra node. The emissivity of the surface (input as material property EMIS for the material number of the element) is used for the radiation surface conductivity matrix. The form factor FORMF and the Stefan-Boltzmann constant SBCONST are also used for the radiation surface conductivity matrix. The form factor can be either input as a real constant (defaults to 1) using KEYOPT(9) = 1 or it can be calculated automatically as a cosine effect using KEYOPT(9) = 2 or 3. For information on how the cosine effect depends on basic element orientation and the extra node location, see the Mechanical APDL Theory Reference. There is no distance effect included in the cosine effect. For axisymmetric analyses, the automatic form factor calculation is used only with the extra node on the Y-axis. The Stefan-Boltzmann constant defaults to 0.119x10^-10 (Btu/hr*in²* °R⁴).

When KEYOPT(4) = 0, an edge with a removed midside node implies that the temperature varies linearly, rather than parabolically, along that edge. See Quadratic Elements (Midside Nodes) in the Modeling and Meshing Guide for more information about the use of midside nodes.

If a single PLANE element lies beneath SURF151, you can automatically set the element behavior (plane stress, axisymmetric, or plane stress with thickness [including TKPS if applicable]) to that of the underlying solid element using KEYOPT(3) =10. This option is valid only when a single PLANE element lies beneath the SURF element. For example, if you apply a SURF151 element over a PLANE77 (thermal) element whose nodes are also used in the definition of a PLANE183 (structural) element, a warning appears and the load is not applied to the element.

A summary of the element input is given in "SURF151 Input Summary". A general description of element input is given in Element Input. For axisymmetric applications see Harmonic Axisymmetric Elements.

SURF151 Output Data

The solution output associated with the element is in two forms:

Convection heat flux is positive out of the element; applied heat flux is positive into the element. A general description of solution output is given in Solution Output. See the Basic Analysis Guide for ways to view results.

The Element Output Definitions table uses the following notation:

A colon (:) in the Name column indicates that the item can be accessed by the Component Name method (ETABLE, ESOL). The O column indicates the availability of the items in the file Jobname.OUT. The R column indicates the availability of the items in the results file.

In either the O or R columns, “Y” indicates that the item is always available, a number refers to a table footnote that describes when the item is conditionally available, and “-” indicates that the item is not available.

Table 151.3: SURF151 Item and Sequence Numbers lists output available through the ETABLE command using the Sequence Number method. See The General Postprocessor (POST1) in the Basic Analysis Guide and The Item and Sequence Number Table in this reference for more information. The following notation is used in Table 151.3: SURF151 Item and Sequence Numbers:

SURF151 Assumptions and Restrictions

SURF151 Product Restrictions

When used in the product(s) listed below, the stated product-specific restrictions apply to this element in addition to the general assumptions and restrictions given in the previous section.

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